Uncatalyzed Growth Mechanisms of Silicon Carbide µ-Fibres

The following project investigates, on a scientific-systematic basis, the growth of silicon carbide microfibers, when no metal catalyst is present. Silicon carbide is a semiconductor that can be synthesized by the de-oxidation of silica using carbon at high temperatures, typically above 1500 C. Under certain conditions, this process leads to the formation of silicon carbide microfibers, which are fibers that are typically some micrometer thick and may reach length scales up to several mm. These silicon carbide microfibers are potentially interesting in a broad range of different applications such as in sensors, field emitters, light emitting diodes, photovoltaics, as well as catalysis and batteries. Prior to the potential use of silicon carbide microfibers in real-life applications, however, a large number of questions, regarding its growth mechanism and chemical composition, remains to be answered. Questions such as: How are initial silicon carbide nuclei formed from the gas phase and can nuclei form on a non-carbon surface? How is the growth initiated without a catalyst and which factors determine the fiber diameter and length? How are dopants incorporated into the silicon carbide microfibers and how does this depend on the dopants chemical nature? What are the important chemical reactions involved? All these questions are going to be addressed within the frame of this project. Therefore, this project is able to fill an important knowledge gap in the field of semiconductor physics. It is in its present form, very important to provide the necessary fundamental understanding for silicon carbide microfibers growth, and consequently, their potential applications.

Our project uncovers how singlecrystal silicon carbide (SiC) microfibres can grow without metal catalysts and how their surfaces and electrical properties can be tailored-knowledge that points to more affordable, robust materials for batteries, sensors and other technologies. SiC is a durable semiconductor that can withstand high temperatures and harsh environments. In our earlier work, we observed that SiC can form needlelike fibres-often millimetres long and only a few micrometres wide-during a heattreatment route starting from a siliconoxygencarbon glass. These fibres are single crystals (the 3C polytype) and show a characteristic hexagonal crosssection. This unusual growth happens without any liquid metal catalyst, which is common in other nanowire processes. These findings raised fundamental questions: where do the fibres start, what makes them grow in one direction, how do dopants enter, and how can we avoid insulating surface oxides? In MICROS, we investigated this growth in a custom inductionheated reactor. A siliconoxygencarbon glass acts as a solid precursor that releases gaseous building blocks when heated. These gases rise to a carbon surface placed above and react there to form SiC, enabling onedirectional fibre growth. This indirect, vapoursolid pathway-without a metal catalyst-offers a simpler route than conventional chemical vapour deposition and could lower costs while yielding larger quantities of doped fibres. We combined systematic growth experiments with insitu and exsitu analysis to track how fibres start and evolve, how dopants are incorporated, and how surfaces form. Among our prior observations carried forward in MICROS is that aluminiumdoped SiC can show a hydrogensaturated, graphenelike surface instead of the usual insulating oxide-an attractive feature for electrical contact and stability. In contrast, nitrogendoped samples tended to form an oxide layer. These differences suggest that dopant chemistry can steer surface endings, a key lever for device performance. Because many reactions happen at extreme temperatures and in parallel, we complemented experiments with kinetic Monte Carlo (kMC) modelling. This allowed us to tease apart which chemical steps and local surface features most strongly influence nucleation and steady, onedirectional growth. By linking observed fibre shapes and compositions to modelled reaction probabilities, we gained a clearer picture of how to trigger growth where and when we want it-an essential step toward controlled fabrication. Long, robust, conductive SiC fibres can be integrated into textiles or bundled into electrodes that are easy to handle and connect. Potential uses include nextgeneration batteries, sensors, catalysis, light emitters and solar cells. Understanding and controlling this metalfree growth mechanism paves the way for reliable, scalable production of tailored SiC microfibres-bringing advanced materials closer to everyday technologies.